Bottom Line:
In control rat pups a majority of cells labeled on E14 were localized in the lower cortical layers V-VI while the cells labeled on E18 were mainly found in the superficial cortical layers II-III.In rat pups subjected to hypoxia on E18, the total number of labeled cells in the parietal cortex was also decreased but the number of scattered labeled neurons was higher in the lower cortical layers.Hypoxia on E18 does not significantly affect cortical structure and parietal cortex-dependent behavioral tasks.

ABSTRACTLong-term effects of prenatal hypoxia on embryonic days E14 or E18 on the number, type and localization of cortical neurons, density of labile synaptopodin-positive dendritic spines, and parietal cortex-dependent behavioral tasks were examined in the postnatal ontogenesis of rats. An injection of 5'ethynyl-2'deoxyuridine to pregnant rats was used to label neurons generated on E14 or E18 in the fetuses. In control rat pups a majority of cells labeled on E14 were localized in the lower cortical layers V-VI while the cells labeled on E18 were mainly found in the superficial cortical layers II-III. It was shown that hypoxia both on E14 and E18 results in disruption of neuroblast generation and migration but affects different cell populations. In rat pups subjected to hypoxia on E14, the total number of labeled cells in the parietal cortex was decreased while the number of labeled neurons scattered within the superficial cortical layers was increased. In rat pups subjected to hypoxia on E18, the total number of labeled cells in the parietal cortex was also decreased but the number of scattered labeled neurons was higher in the lower cortical layers. It can be suggested that prenatal hypoxia both on E14 and E18 causes a disruption in neuroblast migration but with a different outcome. Only in rats subjected to hypoxia on E14 did we observe a reduction in the total number of pyramidal cortical neurons and the density of labile synaptopodin-positive dendritic spines in the molecular cortical layer during the first month after birth which affected development of the cortical functions. As a result, rats subjected to hypoxia on E14, but not on E18, had impaired development of the whisker-placing reaction and reduced ability to learn reaching by a forepaw. The data obtained suggest that hypoxia on E14 in the period of generation of the cells, which later differentiate into the pyramidal cortical neurons of the V-VI layers and form cortical minicolumns, affects formation of cortical cytoarchitecture, neuronal plasticity and behavior in postnatal ontogenesis which testify to cortical dysfunction. Hypoxia on E18 does not significantly affect cortical structure and parietal cortex-dependent behavioral tasks.

Figure 1: Behavioral testing of control rats and rats subjected to prenatal hypoxia on E14 and E18. (A) Development of the whisker placing reaction during the first month of postnatal ontogenesis on P0-P20. Data presented as the mean of whisker placing score ± SEM. Small asterisks and large asterisks—significant (p ≤ 0.05 and p ≤ 0.001, correspondingly) difference compared to control rats. Small cross and large cross—significant (p ≤ 0.01 and p ≤ 0.001, correspondingly) difference between the groups of rats exposed to hypoxia on E14 and E18. (B) Ability of young (dark columns) and adult (white columns) rats to learn an instrumental reflex presented as percent of animals which learn the task well from the total amount of animals taken as 100%. *Significant (p ≤ 0.05) difference between the control rats and rats subjected to hypoxia on E14. + and ++-significant (p ≤ 0.05 and p ≤ 0.01, correspondingly) difference between two groups of rats exposed to hypoxia on E18 and on E14.

Mentions:
Analyzing animal motor reactions during the first postnatal month (from P0 to P20) we have observed that the pups exposed to prenatal hypoxia on E14 had a significant delay in the development of the whisker placing reaction compared to controls and pups subjected to prenatal hypoxia on E18. The animals subjected to prenatal hypoxia on E14 compared to control rats or rats exposed to hypoxia on E18 starting from P0 had a significantly lower score of forelimb placing after stimulation of their whiskers and this difference practically disappeared at P20 (Figure 1A). It indicates a disruption in development of the sensorimotor coordination caused by prenatal hypoxia on E14 but not on E18.

Figure 1: Behavioral testing of control rats and rats subjected to prenatal hypoxia on E14 and E18. (A) Development of the whisker placing reaction during the first month of postnatal ontogenesis on P0-P20. Data presented as the mean of whisker placing score ± SEM. Small asterisks and large asterisks—significant (p ≤ 0.05 and p ≤ 0.001, correspondingly) difference compared to control rats. Small cross and large cross—significant (p ≤ 0.01 and p ≤ 0.001, correspondingly) difference between the groups of rats exposed to hypoxia on E14 and E18. (B) Ability of young (dark columns) and adult (white columns) rats to learn an instrumental reflex presented as percent of animals which learn the task well from the total amount of animals taken as 100%. *Significant (p ≤ 0.05) difference between the control rats and rats subjected to hypoxia on E14. + and ++-significant (p ≤ 0.05 and p ≤ 0.01, correspondingly) difference between two groups of rats exposed to hypoxia on E18 and on E14.

Mentions:
Analyzing animal motor reactions during the first postnatal month (from P0 to P20) we have observed that the pups exposed to prenatal hypoxia on E14 had a significant delay in the development of the whisker placing reaction compared to controls and pups subjected to prenatal hypoxia on E18. The animals subjected to prenatal hypoxia on E14 compared to control rats or rats exposed to hypoxia on E18 starting from P0 had a significantly lower score of forelimb placing after stimulation of their whiskers and this difference practically disappeared at P20 (Figure 1A). It indicates a disruption in development of the sensorimotor coordination caused by prenatal hypoxia on E14 but not on E18.

Bottom Line:
In control rat pups a majority of cells labeled on E14 were localized in the lower cortical layers V-VI while the cells labeled on E18 were mainly found in the superficial cortical layers II-III.In rat pups subjected to hypoxia on E18, the total number of labeled cells in the parietal cortex was also decreased but the number of scattered labeled neurons was higher in the lower cortical layers.Hypoxia on E18 does not significantly affect cortical structure and parietal cortex-dependent behavioral tasks.

ABSTRACTLong-term effects of prenatal hypoxia on embryonic days E14 or E18 on the number, type and localization of cortical neurons, density of labile synaptopodin-positive dendritic spines, and parietal cortex-dependent behavioral tasks were examined in the postnatal ontogenesis of rats. An injection of 5'ethynyl-2'deoxyuridine to pregnant rats was used to label neurons generated on E14 or E18 in the fetuses. In control rat pups a majority of cells labeled on E14 were localized in the lower cortical layers V-VI while the cells labeled on E18 were mainly found in the superficial cortical layers II-III. It was shown that hypoxia both on E14 and E18 results in disruption of neuroblast generation and migration but affects different cell populations. In rat pups subjected to hypoxia on E14, the total number of labeled cells in the parietal cortex was decreased while the number of labeled neurons scattered within the superficial cortical layers was increased. In rat pups subjected to hypoxia on E18, the total number of labeled cells in the parietal cortex was also decreased but the number of scattered labeled neurons was higher in the lower cortical layers. It can be suggested that prenatal hypoxia both on E14 and E18 causes a disruption in neuroblast migration but with a different outcome. Only in rats subjected to hypoxia on E14 did we observe a reduction in the total number of pyramidal cortical neurons and the density of labile synaptopodin-positive dendritic spines in the molecular cortical layer during the first month after birth which affected development of the cortical functions. As a result, rats subjected to hypoxia on E14, but not on E18, had impaired development of the whisker-placing reaction and reduced ability to learn reaching by a forepaw. The data obtained suggest that hypoxia on E14 in the period of generation of the cells, which later differentiate into the pyramidal cortical neurons of the V-VI layers and form cortical minicolumns, affects formation of cortical cytoarchitecture, neuronal plasticity and behavior in postnatal ontogenesis which testify to cortical dysfunction. Hypoxia on E18 does not significantly affect cortical structure and parietal cortex-dependent behavioral tasks.